1. Field of the Invention
This invention relates to a composite material for storage of a radiation image, which comprises a radiation image storage panel.
2. Description of the Prior Art
As is well known, there is widely used a method of radiography wherein an X-ray photographic film is exposed to a radiation passing through an object to record an X-ray transmission image of the object for viewing, particularly for diagnostic purposes. In the conventional radiography, intensifying screens are used together with the X-ray photographic film in order to increase the speed of the radiographic system. In general, the radiography is conducted by interleaving the X-ray photographic film between two intensifying screens, loading the obtained combination in a light-shielding cassette, and loading the cassette in an image recording stage.
However, in mammography, dental image recording or the like, it is impossible to use the cassette as described above. In such a case, therefore, a radiation image is recorded by inserting the X-ray photographic film and the intensifying screens in a light-shielding, bag-like holder. However, in this method, since the X-ray photographic film and the intensifying screens are simply inserted into the holder and not put into close contact with each other, the image quality of the obtained X-ray transmission image is deteriorated, and it is not possible to obtain an X-ray transmission image suitable for viewing, particularly for diagnostic purposes. This presents a very real problem particularly when the X-ray photographic film and the intensifying screens are bent according to the shape of the object in dental panoramic image recording from the outside of the mouth, or the like. In order to eliminate the problem due to loose contact of the X-ray photographic film with the intensifying screens, there has heretofore been used a method wherein the bag-like holder is evacuated to improve contact of the X-ray photographic film with the intensifying screens. However, it is very troublesome to evacuate the bag-like holder, and formation of the bag-like holder capable of being evacuated results in higher costs for image recording.
A novel method for recording and reproducing a radiation image without using the X-ray photographic film is disclosed, for example, in U.S. Pat. No. 4,239,968. In this radiation image recording and reproducing method, there is used a radiation image storage panel comprising a stimulable phosphor which emits light when stimulated by an electromagnetic wave selected from among visible light and infrared rays after exposure to a radiation. (The term "radiation" as used herein means electromagnetic wave or corpuscular radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, high energy neutron rays, cathode rays, vacuum ultraviolet rays, ultraviolet rays, or the like.) The method comprises the steps of (i) causing the stimulable phosphor of the panel to absorb the radiation energy corresponding to the amount of the radiation passing through an object, thereby to form a latent radiation image in the stimulable phosphor, (ii) scanning the panel with an electromagnetic wave such as visible light or infrared rays (hereinafter referred to as "stimulating rays") to sequentially release the radiation energy stored in the panel as light emission, and (iii) detecting the emitted light and converting it into an image.
The radiation image storage panel employed in the aforesaid method for recording and reproducing a radiation image has a phosphor layer comprising an appropriate binder and a stimulable phosphor dispersed therein. When the phosphor layer is self-supporting, the phosphor layer can by itself form the radiation image storage panel. In general, however, the phosphor layer is provided on an appropriate substrate to form the radiation image storage panel. Normally, a protective film for physically and chemically protecting the phosphor layer is provided on the phosphor layer on the side opposite to the substrate. Further, a prime-coating layer is sometimes formed between the phosphor layer and the substrate for the purpose of increasing contact therebetween, a light-reflecting layer is sometimes formed between the phosphor layer and the substrate to improve the sensitivity of the panel, or a light-absorbing layer is sometimes formed between the phosphor layer and the substrate to improve the sharpness of the image obtained by the panel. Further, to improve the sharpness of the image obtained by the panel, the phosphor layer is sometimes colored, or white particles are sometimes dispersed in the phosphor layer.
In the aforesaid method for recording and reproducing a radiation image, a radiation image is stored in the phosphor layer itself of the radiation image storage panel. Namely, the panel is not combined with an X-ray photographic film as in the case of the intensifying screens. Therefore, this method does not present the aforesaid problem due to loose contact of the X-ray photographic film with the intensifying screens. Accordingly, this method can provide a radiation image having high image quality even when image recording is conducted without using the cassette. However, since it is a property of the radiation image storage panel that the radiation energy stored in the phosphor layer is lost as light emission when exposed to stimulating rays, the phosphor layer of the panel should be shielded from light, as in the case of the conventional X-ray photographic film, between the image recording step and the image read-out step so that the phosphor layer will not be exposed to stimulating rays contained in natural light.
Accordingly, when the radiation image storage panel is used for image recording without using the cassette, the panel should be carefully handled, for example in a dark room, so that the phosphor layer of the panel will not be exposed to stimulating rays between the image recording and the image read-out.